The Inner Planets / Study Guide

The Inner Planets / Study Guide

The inner planets are Mercury, Venus, Earth, and Mars. They are small and dense with solid, rocky surfaces. The inner planets are also known as the terrestrial planets. This table below contains more detailed information about each of the inner planets.

Multiple Choice

The word "terrestrial" comes from the Latin word terra. Based on what you know about the inner planets, what does the word terra mean?

• sky

• water

• earth

• ice

Multiple Choice

Which of the inner planets is marked "A" on the diagram at left?

• Mercury

• Mars

• Earth

• Venus

Multiple Choice

Which of the inner planets is marked "B" on the diagram at left?

• Mercury

• Mars

• Earth

• Venus

Multiple Choice

Which of the inner planets is marked "C" on the diagram at left?

• Mercury

• Mars

• Earth

• Venus

Multiple Choice

Which of the inner planets is marked "D" on the diagram at left?

• Mercury

• Mars

• Earth

• Venus

Multiple Choice

According to the table at left (click to enlarge), _______ has the shortest period of rotation.

• Mercury

• Venus

• Earth

• Mars

Multiple Choice

According to the table at left (click to enlarge), _______ has the longest period of rotation.

• Mercury

• Venus

• Earth

• Mars

Multiple Choice

According to the table at left (click to enlarge), _______ has the shortest period of revolution.

• Mercury

• Venus

• Earth

• Mars

Multiple Choice

According to the table at left (click to enlarge), _______ has the longest period of revolution.

• Mercury

• Venus

• Earth

• Mars

Mercury

Mercury is the smallest planet in the solar system and is not much larger than Earth's Moon. Because Mercury is so small, its gravity is too weak to maintain an atmosphere. Therefore, Mercury has virtually no atmosphere. Mercury is also one of the two planets that do not have any moons.

Mercury's surface is similar in appearance to Earth's Moon. Its surface is covered by many craters, which were formed by meteoroid and asteroid impacts. Volcanoes on Mercury's surface also left behind craters and plains. Mercury has a very slow rotation and little atmosphere, which cause extreme temperature ranges on its surface.

A day on Mercury lasts about 59 Earth days. This means that part of Mercury is facing the sun for almost 29 days, allowing the temperatures to rise to 430 degrees Celsius during the day.  Because Mercury has relatively little atmosphere, the heat from the day escapes the planet at night, causing temperatures to drop as low as -170 degrees Celsius.

Multiple Select

Select the words that describe Mercury from those listed below. Check all that apply.

• extreme temperatures

• smallest planet

• dwarf planet

• closest to the Sun

• mild temperatures

Multiple Select

Select the statements below that correctly describe Mercury.

Multiple Select

Why do the temperatures on Mercury vary so greatly?

• Mercury's atmosphere traps in most of the heat from the Sun.

• Mercury does not have a moon.

• Mercury's lack of atmosphere lets most of the Sun's heat escape.

• Mercury has a very slow rotation.

Venus

Venus is sometimes called "Earth's twin," because Venus is similar in size and mass to Earth. Venus is about 87% of the volume of Earth.

The similarities between Earth and Venus end with their sizes. Like Mercury, Venus does not have any moons. Venus as a very thick and cloudy atmosphere that is made up of mostly carbon dioxide. The clouds are made up of sulfur dioxide and drops of sulfuric acid. Venus's atmosphere is extremely heavy. In fact, the pressure of the atmosphere on Venus is about 90 times greater than the atmosphere on Earth. This means that a human standing on Venus's surface would be quickly crushed.

Venus has the hottest surface of any planet. Venus has a greenhouse effect similar to that of Earth. The greenhouse effect is a process in which carbon dioxide in Venus's atmosphere traps infrared heat fom the Sun. This leads to an average surface temperature of about 465 degrees Celsius, which is hot enough to melt lead!

Scientists have learned that the surface of Venus is covered in craters and volcanoes. Space probes that landed on the surface of Venus took pictures of the planet, which showed over 1,600 volcanoes covering its surface. Scientists are still debating whether or not there are active (or erupting) volcanoes on Venus.

Multiple Choice

Compared to Earth, Venus is _________.

• much smaller

• about the same size

• much larger

Multiple Choice

Venus has much ________ temperatures than Earth.

• colder

• hotter

Multiple Choice

Venus's _________ atmosphere is made up mostly of ________.

• thin; nitrogen

• thin; carbon dioxide

• thick; oxygen

• thick; carbon dioxide

• thick; nitrogen

Multiple Choice

Venus has such high temperatures because it is the closest planet to the Sun.

Multiple Select

Which of the following are reasons that a person would not survive very long on Venus? Select all that apply.

• It has temperatures hot enough to melt lead.

• It's extremely dense atmosphere would crush a person in a short amount of time.

• It has active volcanoes that are constantly erupting lava over the surface.

• The clouds on Venus are made of harsh sulfuric acid.

Earth is different from the other terrestrial planets. As far as scientists know, Earth is the only planet in the solar system with the combination of factors known to support life. Life as we know it requires liquid water and an energy source, and Earth has both.

The average temperature on Earth is around 16 degrees Celsius, which allows liquid water to exist. Earth is located in what is known as the "Goldilocks Zone", a zone which is at a distance from the Sun where the temperature is "just right" for liquid water to be present. If Earth were closer to the Sun, it would raise Earth's temperatures and cause the liquid water to evaporate. If it were farther away, it would be so cold that the liquid water would freeze and turn to ice.

Earth is the largest of the inner, terrestrial planets. Seventy percent of Earth's surface is covered in liquid water. Earth's crust and its continents are made up of different types of rocks. Earth has the most surface gravity of the inner planets, so it is able to hold in more types of gases than the other inner planets. These gases make up Earth's atmosphere.

Seventy-eight percent of Earth's atmosphere is oxygen, which animals depend on to breath. The remaining one percent of Earth's atmosphere is a mixture of gases such as carbon dioxide and water vapor. Plants depend on the carbon dioxide in the atmosphere, as it allows them to produce energy through photosynthesis.

Multiple Select

Which components of Earth's atmosphere help to support life on Earth? Select all that apply.

• carbon dioxide

• oxygen

• helium

• hydrogen

• sulfuric acid

Multiple Choice

Why is Earth able to hold onto the mixture of gases that supports life while Mercury is not?

• Earth's rotation is much faster than Mercury's rotation.

• Earth orbits the Sun much more slowly than Mercury.

• Earth has a rocky surface, and Mercury does not.

• Earth has a stronger gravitational pull than mercury.

Multiple Choice

Scientists have discovered another solar system that contains planets that may be located in a habitable zone. In this solar system, the planets orbit around a star known as Gliese 581. According to the image at left (click to enlarge), which of the following determines if a planet is in a habitable zone?

• composition

• period of rotation

• size

• distance from a star

Aside from Earth, scientists have explored Mars than any other planet. They have discovered that there is frozen water in Mars's polar ice caps. Their observations have also led them to believe that there is liquid water beneath Mars's surface that sometimes leaks out onto the surface.

The Martian surface is covered mostly in dark, volcanic rock. Mars is known as the red planet because it is covered in a powdery red dust. This dust is produced from chemical reactions in rocks that are rich in iron. Mars also has many mountains, volcanoes, and craters on its surface. Scientists are still searching for clues as to whether there could be microscopic life on Mars.

Mars has about 10% of the mass of Earth, and is a little over 50% of the diameter of Earth. It is much farther from the Sun than Earth and is therefore much colder. The temperature ranges from -140 degrees Celsius to 20 degrees Celsius.

Mars has a very thin atmosphere made of mostly carbon dioxide. Scientists believe the atmosphere of Mars may be thin due to the solar wind of the Sun. In the winter, the temperatures at Mars's poles become so cold that the carbon dioxide in the atmosphere actually freezes. Mars has two very small moons. They are both covered in craters like Earth's Moon.

Multiple Choice

Mars is called the _______ planet because of the _______ that covers its surface.

• dwarf; dust

• red; gas

• giant; water

• red; dust

• ringed; ice

Multiple Choice

The dust on Mars is a result of chemical reactions of rocks that are rich in ________.

• calcium

• iron

• sulfuric acid

• helium

Multiple Choice

Which of these Martian features does Earth not have.

• two moons

• oceans of water

• one moon

• frozen ice caps

• rocky surface

Multiple Select

Which of these features are unique to both Earth and Mars? Check all that apply.

• frozen ice caps

• one moon

• oceans of water

• rocky surface

• two moons

Multiple Choice

What is the correct order of the inner planets from smallest (in size) to largest?

• Mercury, Venus, Earth, Mars

• Mars, Venus, Earth, Mercury

• Mercury, Mars, Venus, Earth

• Earth, Venus, Mars, Mercury

Multiple Choice

Which planet has an atmosphere of nitrogen, oxygen, and other gases?

• Mercury

• Venus

• Earth

• Mars

Multiple Choice

Which planet has virtually no atmosphere?

• Earth

• Mars

• Venus

• Mercury

Multiple Select

Planets that are closer to the Sun have shorter orbits than planets that are farther than the Sun. Which of the following conclusions about the terrestrial planets can be drawn based on the table at left? (click to enlarge). Select all that apply.

• Mars has the slowest orbit around the Sun.

• Mercury has the slowest orbit around the Sun.

• Mars has the fastest orbit around the Sun.

• Mercury has the fastest orbit around the Sun.

Multiple Choice

A planet's distance from the Sun determines if its temperature allows liquid water to exist. Which bowl would describe Earth's temperature in relation to the presence of liquid water?

Multiple Choice

A planet's distance from the Sun determines if its temperature allows liquid water to exist. Which bowl would describe Venus's temperature in relation to the presence of liquid water?

Multiple Choice

A planet's distance from the Sun determines if its temperature allows liquid water to exist. Which bowl would describe Mars's temperature in relation to the presence of liquid water?

Multiple Select

Which of the following words or phrases describe the inner planets? Check all that are true.

• made of gas

• smallest planets

• rocky

• dense

• largest planets

Multiple Choice

Why does Venus have such a high temperature?

• The carbon dioxide in its atmosphere traps heat.

• It has many active volcanoes on its surface

• It is the closest planet to the Sun.

• All of the above

Multiple Select

Which of the following statements describe Mercury? Check all that are true.

• Its surface is covered in craters.

• It is the smallest planet

• It has little or no atmosphere.

• It does not have a moon.

Multiple Choice

Which of the following allow Earth to support life?

• the temperature

• the presence of liquid water on its surface

• the atmosphere

• all of the above